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Vibrio parahaemolyticus has been the most common food-borne pathogen in southern China, especially the O3:K6 pandemic clone and its serovariants. Recently, the serotype O4:K8 became more and more prevalent in southern China, which was different from the O3:K6 pandemic clone. Thus, the aim of the present work was to elucidate the molecular characteristics of the O4:K8. Some O3:K6 pandemic clone and its serovariants isolated in the same period were selected for comparative analysis, which were still dominant clone locally. The whole genome sequencing (WGS) was applied to characterize 20 strains of V. parahaemolyticus isolated from food-borne diarrheal cases and belonging to the serotype O4:K8, O3:K6 and O1:KUT (untypable), prevalent serotypes in recent southern China. The results showed that all these isolates were positive for the thermostable direct hemolysin gene (tdh), while negative for the TDH-related hemolysin gene (trh). We compared the V. parahaemolyticus strains to those of 31 strains isolated overseas and were available from NCBI genome database. A WGS-SNPs phylogenetic analysis of all the genomes revealed that the strains formed an important genetic lineage, which was genetically distinct from the O3:K6, O1:KUT and other internationals strains. Comparative genome analysis also revealed that all the O4:K8 strains carried the entire T3SS-1 and VpaI-7 (T3SS-2) regions, the most important virulent elements of the O3:K6 pandemic clone. However, all the O4:K8 strains lacked the entire VpaI-1 and VpaI-4 regions and carried only few ORFs of the VpaI-5 and VpaI-6, which were considered to be unique among post-1995 strains belonging to the O3:K6 pandemic clone. Our data showed that the O4:K8 strains possessed the virulence factors similar to the O3:K6 pandemic clone, which may have enabled them to become prevalent in southern China. Our study also revealed that WGS-bases analysis may help improve understanding epidemiology of this bacterium in food-borne disease surveillance., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Objective: To investigate the serotypes, antimicrobial resistance, virulence genes and molecular characteristics of food-borne Vibrio parahaemolyticus isolated in Guangdong province in 2014., Methods: Sixty V. parahaemolyticus strains were tested in this study. The serotyping and antibiotic resistance test were conducted, while the tdh and trh gens of the strains were detected with conventional PCR, and pulsed field gel electrophoresis (PFGE) and multiple locus sequence typing (MLST) were conducted too., Results: The 60 strains belonged to 13 serotypes, the major serotypes included O3: K6, O4: K8, O1: K36 and O4: KUT. The antibiotic resistance test indicated the isolates were highly resistant to ampicillin (100.0%), sulfonamides (43.3%) and cefalotin (28.3%). Up to 56.7%(34/60) of the strains were resistant to two or more antibiotics, and 2 strains showed resistance to three antibiotics. The virulence gene detection indicated that 63.3% (38/60) of the strains carried tdh⁺ trh⁻, while only 1 strain carried tdh⁺ trh⁺. The 60 strains digested by NotI belonged to 48 different PFGE patterns and 3 clusters. The cluster B included the strains isolated from sporadic food borne cases with serotype of O3: K6 and similarity of 62.6%-100.0%. The cluster C included O4: K8 strains with the PFGE pattern similarity of 56.7%-62.5%. The MLST indicated that the 60 strains had 26 sequence types (STs). The ST-3 was predominant, including 33 strains (serotypes O3: K6 and O1 :K36). The four O4: K8 strains formed another predominant colony, which was different from ST-3., Conclusion: The etiologic characteristics of V. parahaemolyticus varied, which might be one of the reasons for high incidence of food-borne V. parahaemolyticus infection in Guangdong. The molecular characteristics of O4: K8 strain were different from the other predominant serotypes. Close attention should be paid to the possible outbreak caused by O4: K8 strain in this area.

Vibrio parahaemolyticus has emerged as a common foodborne pathogen of global concern. In this study, 108 V. parahaemolyticus isolates that recovered from diarrhea cases (n=96) and seafood products (n=12) in Guangdong Province from 2007 to 2011 were characterized by serotyping, tdh and trh toxin gene detection and multilocus sequence typing (MLST). The dominant serotypes from the cases were O3:K6, O4:K8 and O1: KUT (untyped). However, most isolates recovered from seafood products belonged to other serotypes. None of the isolates carried the trh gene, while the major isolates from the cases were tdh positive. MLST analysis revealed 31 sequence types (STs); 17 STs were unique in this study. eBURST analysis revealed four clonal complexes (CC), The majority of the isolates (n=58, all from cases and tdh+) were grouped into the CC3, which included O3:K6, O4:K68 and O1:KUT isolates. The CC3 was the most prevalent clonal complex, and all of the CC3 isolates were recovered from clinical cases of geographically diverse origin. As to the CC345, which was completely constituted by O4:K8, was another important clonal complex affecting Guangdong Province. Ongoing surveillance of V. parahaemolyticus in diarrhea patients and seafood products remains a public health priority for Guangdong Province, China., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Objective: To study the serotypes, antimicrobial resistance, virulence genes and molecular characteristics of Vibrio parahaemolyticus isolated from outbreaks and sporadic cases in Guangdong, 2013., Methods: 36 Vibrio parahaemolyticus strains isolated from outbreaks and 43 strains from sporadic cases were sero-typed and tested for antimicrobial resistance. PCR was used to detect for tdh(thermostable direct hemolysin gene), trh (tdh(-) related hemolysin gene), GS-PCR and orf8 genes. All the samples were analyzed by pulsed-field gel electrophoresis (PFGE)., Results: 36 isolates from outbreaks were all identified as O3 : K6, and among the 43 sporadic isolates, O3 : K6 (23, 53.49%) was the dominant serotype. Vibrio parahaemolyticus isolates showed high resistance rate to ampicillin (96.20%) and cefalotin (40.50%), but were high sensitive to cotrimoxazole (100%) and chloramphenicol (100%). 83.33% (30/36) outbreak isolates were resistant to multi-drugs but only 37.21% (16/43) of the sporadic isolates showed so. Results from virulence gene detection suggested that all the 36 outbreak isolates belonged to tdh(+) trh(-) strains, while 86.05% (37/43) of the sporadic isolates were tdh(+)trh(-) and 11.63% (5/43)were tdh(-)trh(+) . Only one tdh(+)trh(+) strain was found. All the outbreak isolates contained GS-PCR and/or orf8 genes, whereas among the sporadic isolates only 51.16% (22/43) of them carrying the similar genes. Results from PFGE analysis suggested that 79 isolates were discriminated into 3 clusters and 32 different PFGE patterns with the similarity value between 59.8% and 100.0%. Outbreak isolates seemed to gather in the same cluster, while the sporadic isolates spreading in all the three clusters., Conclusion: O3 : K6 was the dominant serotype in Vibrio parahaemolyticus strains isolated in Guangdong, 2013. These strains showed high sensitivity to most antibiotics, but with multi-drug resistance. Positive rate of tdh gene was high, and most O3 : K6 strains contained GS-PCR and/or orf8 genes. PFGE analysis revealed genetic diversity was within the Vibrio parahaemolyticus strains in Guangdong.

Vibrio parahaemolyticus infection has been considered the leading cause of bacterial illnesses mainly associated with seafood consumption in Guangdong province in China. In this study, epidemiological and etiological characteristics of 36 V. parahaemolyticus outbreaks that occurred from 2008 to 2010 in Guangdong province were analyzed; 284 strains involved were characterized by serotyping; virulence genes and 66 strains from four outbreaks therein were subtyped by pulsed-field gel electrophoresis (PFGE). Epidemiological evidence showed that 36% (13/36) of outbreaks were caused by food contamination, of which 84.6 % (11/13) were related to salted food, including viscera of pigs and cattle, meat, and vegetable salad. It was also indicated that 88.9% (32/36) of V. parahaemolyticus outbreaks appeared from June to September, 44.4% (16/36) of which occurred in canteens as well as 41.7% (15/36) in restaurants. As for the etiology, 31% (11/36) of outbreaks were caused by single serovar of strains, while 69% (25/36) were caused by multiserovars; O3:K6, O4:K8, O1:Kut, and O2:K3 were the dominant serovars. Among the 284 strains, 98.8% (254/257) of strains from patients were tdh-present and trh-absent, whereas 37.0% (10/27) from food were tdh-present. Cluster analysis of PFGE patterns demonstrated that strains in the same outbreak with identical serovar seemed to be diversified, whereas strains with various serovars could be closely related genetically. Moreover, cross-contamination between salted food and seafood was first confirmed by molecular subtyping in Guangdong, revealing that salted food might be a vital risk factor associated with V. parahaemolyticus outbreaks.